Start/stop (S/S) vehicles typically deactivate the vehicle engine when the vehicle comes to an idle stop. Such an action is prevalent in city driving, in order to conserve fuel economy. Hybrid electric vehicles (HEVs) are similar to S/S vehicles, and can drive in battery mode for a limited time. In HEVs and S/S vehicles, while the engine is shut off the fuel pump is also typically turned off.
However, some environmental conditions such as high ambient temperature conditions, and rapid changes in elevation, may impact the boiling point of fuel. For example, a common failure of high flow fuel systems is cavitation, or vapor lock, which may result in liquid fuel vaporizing (boiling) inside the fuel pump assembly. If cavitation occurs in a vehicle fuel pump, symptoms may include dramatic loss of fuel flow rate, inconsistent or loss of fuel pressure, ratchet or grinding sounds from the fuel pump, etc. Thus, if the fuel pump is turned off at an idle stop under conditions where fuel temperature is high, and in some examples, where the vehicle has experienced a rapid elevation change to a higher altitude, vehicle performance may be impacted. For example, the pump may be unable to recover fuel pressure in time once cavitation occurs, which may thus result in a potential vehicle stall condition. The inventors herein have recognized these issues.
Furthermore, loss of fuel delivery pressure may result in a lean-out condition that may result in the engine being compromised. In another example, exposure of a vehicle fuel pump to cavitation conditions may in some examples affect the operation of the fuel pump itself. For example, the fuel pump may experience a loss of capacity and efficiency, depending on the severity of the cavitation exposure. The inventors herein have additionally recognized these issues.
U.S. Pat. No. 8,326,479 teaches that in a deceleration fuel shut-off (DFSO) mode, fuel injectors may be turned off, but the fuel pump may remain powered if pressure in the fuel line is below a predetermined threshold. More specifically, a pressure sensor may be used to determine if pressure in the fuel line is at or above a predetermined threshold during the DFSO mode, and if pressure is below the threshold, power to the fuel pump may be maintained. However, the inventors herein have recognized potential issues with such an approach. For example, under circumstances where potential fuel pump cavitation may occur while the engine is off responsive to a DFSO event, it may be desirable to control fuel pump speed to prevent potential fuel pump cavitation, even if pressure in the fuel line is above the predetermined threshold. Furthermore, while U.S. Pat. No. 8,326,479 teaches controlling a fuel pump during DFSO conditions, it is not taught to control the fuel pump during idle stop events, which may represent another condition where fuel pump cavitation may occur while the engine and fuel pump are off. Still further, U.S. Pat. No. 8,326,479 does not teach controlling or regulating the fuel pump during either DFSO events or idle stop events, responsive to potential stall conditions, where potential stall conditions may include one of at least high ambient (and fuel) temperature, and rapid increase in elevation of the vehicle.
The inventors herein have recognized these issues, and have developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising propelling a vehicle at least in part by an engine that combusts fuel provided to the engine via a fuel pump; controlling fuel injection to one or more engine cylinders via one or more fuel injectors; monitoring the engine for a potential stall condition while the engine is combusting fuel; and controlling the fuel pump at a fuel shut-off event based on whether the potential stall condition is indicated.
In an example, pressure in a fuel rail may be monitored responsive to the fuel shut-off event, where the fuel pump is configured to provide pressurized fuel to the fuel rail prior to the fuel being delivered to the one or more fuel injectors. One example includes stopping the fuel pump responsive to pressure in the fuel rail above a predetermined fuel rail pressure threshold, and further responsive to the potential stall condition not being indicated. Another example includes maintaining power to the fuel pump responsive to pressure in the fuel rail below the predetermined fuel rail pressure threshold, and further responsive to the potential stall condition not being indicated. In such an example, maintaining power to the fuel pump may include controlling a fuel pump speed, wherein the fuel pump speed is controlled as a function of indicated pressure in the fuel rail and wherein the fuel pump is stopped responsive to pressure in the fuel rail reaching the predetermined fuel rail pressure threshold during the fuel shut-off event. Still another example includes maintaining power to the fuel pump responsive to the potential stall condition being indicated, and independent of pressure in the fuel rail. In such an example, maintaining power to the fuel pump may include controlling fuel pump speed to a minimum speed, where the minimum speed comprises a lowest amount of power provided to the pump that maintains fuel flowing across the fuel pump. By controlling fuel pump speed to the minimum speed when a potential stall condition (e.g. combustion instability) is indicated, fuel pump cavitation may be prevented without compromising battery power. By preventing fuel pump cavitation, engine and fuel pump complications may be avoided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.